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<p>The enormous wind stress associated with a cyclone will induce strong mixing in the upper ocean. Mixing between the warm mixed layer water and the colder thermocline water can significantly reduce the Sea Surface Temperature (SST) and, in turn, heat transfer across the air-sea interface. The enhanced mixed layer cooling and the reduction in the enthalpy fluxes may finally lead to the weakening of the cyclone. Hence, understanding the mechanisms behind mixed layer cooling and the SST feedback between the ocean and cyclones is essential for intensity prediction. The present study attempts to understand the oceanic process behind the mixed layer cooling during the depression stage of the cyclone ‘Nanauk’ in the Arabian Sea (AS). In situ observations from the moored buoy at eastcentral AS, near the cyclone track, are used to understand the temporal variability of mixed layer temperature, mixed layer depth (MLD), and the Depth of 26&#xa0;°C (D26&#xa0;°C) isotherm. The one-dimensional mixed layer model PWP is used to simulate temperature and MLD variability during the direct wind forcing period. The model simulations and observations are consistent during the initial phase of the forcing period. The present study shows that even though wind stress during the depression stage of a cyclonic storm is weaker, entrainment mixing could significantly contribute to the mixed layer cooling. The elevated temperature gradient at the mixed layer base, a typical seasonal characteristic of AS during the monsoon onset phase, was sufficient to facilitate enhanced vertical turbulent entrainment mixing in the AS.</p>

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The role of entrainment mixing on the mixed layer cooling in the Arabian Sea during the depression stage of the Cyclonic Storm Nanauk

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年8月5日

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  • John K. Lix,
  • R. Sajeev,
  • Ramasamy Venkatesan

摘要

The enormous wind stress associated with a cyclone will induce strong mixing in the upper ocean. Mixing between the warm mixed layer water and the colder thermocline water can significantly reduce the Sea Surface Temperature (SST) and, in turn, heat transfer across the air-sea interface. The enhanced mixed layer cooling and the reduction in the enthalpy fluxes may finally lead to the weakening of the cyclone. Hence, understanding the mechanisms behind mixed layer cooling and the SST feedback between the ocean and cyclones is essential for intensity prediction. The present study attempts to understand the oceanic process behind the mixed layer cooling during the depression stage of the cyclone ‘Nanauk’ in the Arabian Sea (AS). In situ observations from the moored buoy at eastcentral AS, near the cyclone track, are used to understand the temporal variability of mixed layer temperature, mixed layer depth (MLD), and the Depth of 26 °C (D26 °C) isotherm. The one-dimensional mixed layer model PWP is used to simulate temperature and MLD variability during the direct wind forcing period. The model simulations and observations are consistent during the initial phase of the forcing period. The present study shows that even though wind stress during the depression stage of a cyclonic storm is weaker, entrainment mixing could significantly contribute to the mixed layer cooling. The elevated temperature gradient at the mixed layer base, a typical seasonal characteristic of AS during the monsoon onset phase, was sufficient to facilitate enhanced vertical turbulent entrainment mixing in the AS.